For example, during cardiac surgeries, artificial-lung extracorporeal circulation is generally performed in which patient's blood is drawn from the vein (the vena cava) of the patient by a blood pump, and the gas is exchanged by an artificial lung, and then the blood is returned to the artery of the patient.
A circuit for such extracorporeal circulation (an extracorporeal circulation circuit) is equipped with a bubble removing unit for removing (separating) bubbles flowing in the drawn blood. Known bubble removing units include a unit including a housing (container body) and a filter disposed in the housing and partitioning the housing into a blood inflow space (upper space) into which blood flows and a blood outflow space (lower space) from which blood flows out, which applies centrifugal force to the blood to collect bubbles into the center of the housing (blood inflow space) and collects the bubbles to the upper space of the housing by buoyancy, and then removes the bubbles with deaeration means (for example, refer to JP-B-64-8562).
However, with the bubble removing unit, when excessive bubbles (gas) accumulate in the blood inflow space (bubble reservoir), the bubbles sometimes pass through the filter, posing the possibility that the bubbles are not sufficiently (completely) removed, so that they may flow out of the bubble removing unit together with the filtered blood.